Enzootic Pneumonia (EP)

The main issue associated with M. hyopneumoniae infections is chronic respiratory disease. This pathogen usually amplifies the severity of other infections, including flu and PRRS.

Alternative names: Mycoplasma hyopneumoniae


It is a chronic swine disease of big importance globally. Its chronic presentation is frequent in production farms working under continuous flow. The organism grows slowly, thus the disease manifests at 7 or 12 weeks of age, and is part of the porcine respiratory disease complex. It is treated with antibiotics and prevented with vaccination.

Enzootic pneumonia is caused by Mycoplasma hyopneumoniae, a bacteria that does not have cellular wall. It is widely spread in swine populations and is endemic in most of the farms globally. It always attacks the ciliated epithelium in the inferior parts of each lung lobe, producing tissue consolidation (typical of a pulmonary bacterial infection).

The main problem associated to M. hyopneumoniae infections is chronic respiratory disease, which can be associated to a dry and nonproductive cough. The disease has high morbidity and a low mortality, and it has a strong effect on average daily gain and feed conversion ratio.

If enzootic pneumonia is not present in the grower population, the effect of the other pathogens decreases significantly. Thus, it is considered a pathogen that increases the severity of other infections, including influenza and PRRS.

Disease occurs when enzootic pneumonia appears for the first time in a farm. For a period of 2 to 4 weeks after the bacteria enters the farm, an acute intense pneumonia with high mortality in pigs of all ages is observed.

The transmission is mainly through direct contact (nose to nose). The risk of transmission decreases in the farrowing area, with the age of the sows.


Affects all ages but is not clinically frequent in animals 6 weeks or younger. Its incubation period is 2 to 8 weeks.

Clinical symptoms include:

  • Can develop chronic or acute pneumonia.
  • Severe difficulty to breath.
  • Prolonged nonproductive cough.
  • Mortality varies depending on co-infections.

Causes / Contributing Factors

  • Transmitted by the entry of carrier pigs.
  • Airborne in distances up to 9.2 km, weather conditions permitting. The organism dies quickly outside the pig, mainly in dry conditions.

The increase of the clinical disease is associated to the following factors:

  • Too wide pens which do not have a good air flow.
  • Variations in temperature and deficient isolation.
  • Variable air speed, cold.
  • High carbon dioxide and ammonia levels.
  • High dust and bacteria levels in the air. Movement of pigs, stress and mixing animals, especially of different ages.
  • Continuous flow housing systems.
  • Other concurrent diseases specially PRRS, Actinobacillus pleuriopneumoniae, influenza, and Aujeszky’s disease.



Based on clinical signs and post-mortem examinations, sometimes combined with histology of the lesions. However, these tools do not bring a specific diagnosis, and in farms producing reproductive animals or in special cases, it might be necessary to confirm the diagnosis through one or more of the following tests: ELISA, serological tests, microscopical examination of lung stained touch preparations, immunofluorescence tests, PCR and culture and identification of Mycoplasma hyopneumoniae.

These analyses are not available in all laboratories. PCR is the most sensitive method.

Enzootic pneumonia must be differentiated from influenza, PRRS, Glässer disease and other bacterial infections. Laboratory analyses are needed to differentiate them. In addition, all or some of these infections can be present together with Mycoplasma hyopneumoniae.


Diet medication might be necessary if:

  • There is variable growth in pigs from 10 to 20 weeks of age is present.
  • More than 2.5% of the population needs individual treatment.
  • Active lesions that stand out from the lung surface and are humid or wet are present.

In acute outbreaks or endemic herds consider the following factors:

  • Strategically medicate pigs at critical periods of high risk
  • Inject severely affected pigs with antibiotics.

Inactivated vaccines against Mycoplasma hyopneumoniae are very effective if they are administered early (before 5 weeks of age) and when the animals are not exposed to the replication of the PRRS virus.